1. Field of the Invention
The invention relates to a method and device for drying pourable products within a rotor chamber. The pourable products are put into radially peripheral circulation by a rotor having a vertical rotor axis.
The product may basically be of any kind, insofar as it is possible to direct the product into radially peripheral circulation. The product is thus also designated more specifically as a pourable product. In practice, it usually includes product particles which are homogeneous in a material-specific way or cores, to which any desired moist enveloping layer has been applied in previous method steps. The application of a moist enveloping layer may also take place in parallel with drying, in such a way that the enveloping layer is dried immediately during and after application.
Pourable products may, in this context, be all solid particles, fragments or elements which can be put into radially peripheral circulation by a rotor, for example granulates, pellets, grains, tablets, pills and the like. All products of this kind may be homogeneous, agglomerate or a core already provided previously with one or more layers.
An enveloping layer may consist of one substance or of a mixture of a plurality of substances.
2. Description of Related Art
According to the prior art, various methods and devices for drying granulates or pourable products are known.
In fluidized-bed drying methods, a dry gas acts upon the product from below, in such a way that the product is swirled up, the dry air removing the moisture from the products.
JP 07047261 A specifies a device for the treatment of particles by fluidized-bed drying, in which the dry gas is led through a rotating horizontal gas-permeable disk, the gas passage being larger in the outer region than near the axis. The particles located above the disk are moved radially outward as a result of the rotation of the disk and are swirled up by the dry gas.
For the circulation of products in a rotor chamber, for example, DE 4411058 C2 is known. This specifies a device for the coating of granular material, in particular for the coating of seed with chemicals, such as dressing agents.
The device has a conically upwardly widened side wall of a mixing cylinder which rotates at high speed and which is rotatable about a vertical axis. The liquid chemicals are sprayed via a spray device onto the granular material located in the mixing cylinder. For the better intermixing of the granular material in the mixing chamber, bent diverting blades are arranged above the mixing cylinder on a discharge ring, said diverting blades deflecting the material and leading it downward back into the conical mixing cylinder. In this case, the diverting blades are designed in such a way that the granular material is deflected from the outer upper edge of the mixing cylinder into the center.
The solutions according to the prior art all entail the risk that delicate products, or the cores with a delicate enveloping layer which at least temporarily has a moist and therefore soft surface, are subjected to compressive and frictional forces in such a way that the products or the enveloping layers are unacceptably damaged.
The object on which the invention is based, therefore, is to specify a device for drying pourable products, whereby the products can be dried carefully and effectively. In particular, pourable products having a soft and delicate surface layer are capable of being dried. The object is, furthermore, to specify a method for using the device.
In accordance with the invention, the product to be dried is put into radially peripheral circulation in a very careful way and, at the same time, a dry gas is led through sheet like gas passages in the conical shell of the rotor and through the circulating product.
The direction of movement of the product is, in this case, influenced by the rotor, in such a way that the individual particles of the product are moved radially outward and upward and subsequently fall back onto the rotor essentially due to gravity.
According to the invention, the product is deflected into a central direction by guide vanes, on which the product rolls. In a further refinement, the guide vanes may also have an adjusting mechanism, such that the geometry of the guide vanes can be adjusted. The device can consequently be adapted universally to the optimum circulation characteristics of different products with a varying configuration and mass. Devices of this kind may also be used for the compensation of changing mass ratios during drying.
The dry gas flows round the product very effectively and virtually at every point, the product not being exposed to any adverse compressive loads. The type of dry gas, its flow velocity and its temperature are influenced critically by the specific conditions of the respective product.
The device according to the invention is designed, in principle, as a batch-fed plant, since drying requires a certain amount of time. It is also possible, however, to operate the device as an interval flow plant. That is to say, the product to be dried is fed to the rotor chamber at intervals through an inlet orifice and, after an appropriate process duration, is discharged from an outlet orifice again.
In a discharge solution which has proved appropriate in this case, there is at least one flap in the wall of the rotor chamber above the annular gap between the rotor and the rotor chamber, said flap being suitable for moving the products out of the rotor chamber by means of the centrifugal forces when the flap is in the open position and rotor is rotating.
By means of the device according to the invention, delicate products can be dried very effectively and in a simple and careful way. The products, in particular delicate soft paste enveloping layers on cores, are not appreciably deformed during drying and their external configuration has a high degree of uniformity.
The invention is explained in more detail below with reference to an exemplary embodiment.